1. Field of Invention
The present invention relates to an image processing device, an image processing method, and an image processing program for printing by combining recording materials of a plurality of colors such as cyan, magenta, and yellow.
2. Description of Related Art
Color printers that print by overlaying different colors of ink or other recording materials such as cyan, magenta, and yellow are known from the literature. When an inkjet printer, for example, prints on a medium that absorbs fluid ink easily, such as plain paper, for example, different colors of ink blend together and form mixed colors even if the printed data is separated by a dot. When printing on a recording medium that is more resistant to ink absorption, such as synthetic paper, the ink may not be absorbed and may flow over the surface.
Japanese Unexamined Patent Appl. Pub. JP-A-2001-353857 is directed to an inkjet printer that reduces the overlapping portions of ink dots formed on the recording medium to a level that does not result in a drop in print quality. More specifically, first and second ink nozzle rows are offset one-half dot pitch from each other in line with the ink nozzle rows, and the diameter of the ink dots discharged from the ink nozzles and formed on the recording medium is less than the nozzle pitch.
Japanese Unexamined Patent Appl. Pub. JP-A-2002-199236 pertains to an inkjet printer that prints using a cyan (C), magenta (M), yellow (Y), black (K) ink set and can adjust the density of the barcode that is printed. This inkjet printer converts RGB color image data to CYMK image data corresponding to the same output colors using appropriate amounts of cyan (C), magenta (M), yellow (Y), and black (K) ink, and then adjusts the density of the CYMK image data to adjust the barcode density.
Japanese Unexamined Patent Appl. Pub. JP-A-H08-251363 is directed to a printer that produces black using a cyan (C), magenta (M), and yellow (Y) ink set. More specifically, a printer that has a cyan (C), magenta (M), and yellow (Y) ink set combines suitable amounts of cyan (C), magenta (M), and yellow (Y) ink dots printed at the same location to produce a composite black dot without using black (K) ink.
A problem with the printer taught in Japanese Unexamined Patent Appl. Pub. JP-A-2001-353857 is that bleeding between adjacent dots can be extreme depending upon the type of paper used, and the print quality therefore drops accordingly. The amounts of cyan (C), magenta (M), and yellow (Y) ink may be reduced uniformly to reduce such bleeding, but this method also changes the printed color and prevents achieving the desired output.
More particularly, it may not be possible to print and read the correct code from a barcode printed with composite black when bleeding is severe because a barcode is read based on the ratio between the width of the bars and spaces. In addition, if the density of the composite black is adjusted in the image data after color conversion as taught in Japanese Unexamined Patent Appl. Pub. JP-A-2002-199236, quantization error, for example, may occur in the color density adjustment process. As a result, the balance between the colors producing the composite black is disrupted and color shift may occur in the black areas.
This means that if a color density adjustment process is used when printing a barcode with composite black, the color of the barcode may deviate from the intended color and read errors may result when reading the barcode with a barcode reader. The color shift also means that the printed black will not look black and the appearance is poor. However, if the color density is not adjusted in order to prevent such a color shift, excessive ink density may cause the barcode to bleed, thus causing barcode read errors resulting from deviations in the bar width or from insufficient ink density. Repeatedly printing composite black also results in rapid consumption of cyan (C), magenta (M), and yellow (Y) ink.
It is therefore difficult for a printer that prints black by printing composite black to achieve the desired color and density, and it is particularly difficult to print a high quality barcode.